Optical power amplification has relevance to terrestrial and space applications. A well-known terrestrial application requiring optical power amplification is laser radars for missiles. A well-known space application requiring optical power amplification is inter-satellite optical communications. Such applications may require optical power outputs at 10W or higher.
Scaling output power of fiber lasers and amplifiers above a 10W level is a challenging task for a number of reasons. Although fiber lasers and amplifiers operating in a 10-20W range have been demonstrated, such devices use diode pumps with relatively short lifetimes, which rule out the possibility of using diode pumps in space applications. In addition, high power fiber lasers and amplifiers are prone to spontaneous mode locking, Q-switching and high-intensity relaxation oscillations. These processes create spikes of high intensity that damage fiber ends.
One solution to the problem of power scaling fiber lasers and amplifiers can be found in the commonly assigned U.S. patent application Ser. No. 09/574,282 filed May 19, 2000, as referenced above. In this application, controlling the phase of fiber amplifiers has been demonstrated by adjusting the pump power of individual amplifiers. When phase-locked, the output beam in the far zone consists of a number of bright, diffraction-limited spots whose individual intensities are considerably higher than those of a non-locked output.
A need still exists for an apparatus and a method that enables power scaling of an optical system while maintaining beam quality.